There is an ever-increasing demand for miniature highly sensitive sensor devices suitable for manufacturing and industrial processing applications, environmental monitoring, as well as defense and homeland security applications. There is also a need for such devices capable of sensitive detection of biochemical and cellular responses in live cells and organisms. Indeed, the ability to rapidly detect minute concentrations of specific macromolecules is especially suited for clinical diagnostics, genomics, and drug discovery. However, conventional macromolecular sensing systems rely on labels, such as radiolabelled tags or fluorophores. There is currently a need in the art for devices, and methods, capable of label-free sensing. These devices, and methods, would likely significantly decrease the time needed for sample preparation, increase sample analysis throughput, and mitigate the need for target molecules modification.
One of the most promising platforms for label-free sensing is nano-wire field effect transistors (NW-FETs). These sensing devices, having the advantage of enhanced sensitivity due to the nano-scale channel confinement, operate by sensing the intrinsic charge of bound molecular species. For example, by binding a receptor protein or a single-stranded DNA (ssDNA) oligomer to the NW-FET surface, the binding of the specific ligand or complementary ssDNA modifies the electric field surrounding the device, enabling direct electronic detection.
Single-crystal, semiconducting NW-FETs are also attractive as biosensors due to their exquisite sensitivity to bound charge and potential portable format. Nanowire devices configured as solution-phase sensors or ion-sensitive FETs (ISFETs) have been demonstrated as ultrasensitive sensors. For example, solutions with physiologic salt concentrations have ionic (Debye) screening lengths of ˜0.7 nm, which effectively neutralizes the molecular charge of a bound ligand beyond this distance. Thus, detection of such surface-bound ligands requires measurements to be performed in a low salt (1.5 mM) buffer to increase Debye screening lengths.
Although these, and other, silicon-based nano-sensors have been reported, they have exhibited poor sensing capabilities and their fabrication typically requires complex hybrid manufacturing methods having unreliable product performance and consistency. In addition, typical silicon-based nano-wire fabrication processes exhibit relatively poor material and device service life, thereby further discouraging nano-wire sensor incorporation into larger integrated detector systems.
Hence, there is a need for nano-sensor devices having improved sensing characteristics for enabling accurate and efficient detection of specific reagents in minute concentrations. There is also a need for a simplified fabrication process to produce nano-sensor devices having improved sensing capabilities that may be integrated into a variety of signal processing and information systems. Further, there is a need for a method that affects a solution pH change upon specific ligand binding.